The River fire had spread to about 95 acres by midafternoon and prompted the closure of Santa Paula Airport

Ventura County firefighters Monday were battling a fast-moving brush fire in a riverbed near the Santa Paula Airport.

The blaze, called the River fire, had spread to about 95 acres by 3:15 p.m., according to the Ventura County Fire Department.

Air crews were dropping flame retardant on the fire, which was reported about 1 p.m. in the Santa Clara River, Santa Paula Fire Department spokesman Andy VanSciver said via Periscope.

Fire Department video footage showed thick, black smoke coming from the riverbed. VanSciver said the eastward-moving blaze was being fueled by winds and dry brush.

Firefighters spotted an apparent homeless encampment in the riverbed shortly after the blaze started, but it was unclear whether it was occupied, Ventura County Fire Department spokesman Capt. Mike Lindbery said via Periscope.

“Our biggest concern is the potential for homeless encampments in the river bottom,” he said.

An employee at Santa Paula Airport said it was closed Monday afternoon because of the fire and heavy smoke in the area.

South Mountain Road was closed between the 12th Street bridge and Balcom Canyon Road, according to the Ventura County Fire Department.